The present invention relates to a device for automatic spray application of paint through a spray nozzle. This device comprises a unit adapted to be connected and provide paint to the nozzle during the automatic spray application.
Such a device may have different fields of uses. For illuminating, but not in any way restricting the invention, the use of such a device for painting vehicle bodies, with a spray application robot will hereinafter mainly be discussed. Though paints are referred to in this application, this term is given a broad meaning to include paints of all types and varnishes suited for spray application.
Known devices of this type have a number of units providing paint. These units have centrally located paint sources that are positioned remotely with respect to the spray robot. Each unit is intended for a distinct paint source, one for each type of paint and color, and each is connected to the spray nozzle through a ring conduit. The selection of a paint source is controlled by valves arranged on the robot, thereby requiring a large number of valves, often more than 60. The remote location of the paint sources and numerous valves cause several important drawbacks, most especially when many types of paints and colors are to be sprayed by the spray robot. For each paint source, a hose connects the source unit to the spray robot. A large number of hoses running between the centrally located paint sources and the spray robot makes the device expensive and restricts the ability to move the spray robot. Furthermore, since each hose must be cleaned occasionally, using a large number of hoses increases the maintenance for cleaning and removing obstructions from them. Additionally, a large volume of paint is lost when a color or paint type is changed, since the hose lengths are long, the valves and paint control means are complex, and the new paint may not be mixed with the previous paint type.
Another drawback relates to water-born paints, which are more and more frequently used, since these paints have a higher viscosity than oil base paints. A higher pumping pressure is required for pumping higher viscosity paints to the spray robot and the risk of paint being deposited in and obstructing the hoses is increased. Furthermore, considerable problems arise in electrically insulating the paint sources and the spray nozzle when performing electrostatic painting when using water-born paints in conjunction with ring conduits.
The object of the present invention is to provide a device that solves the inconveniences mentioned above of such devices already known.
This object is obtained by a device, having a paint container arranged close to the spray nozzle. Additionally, the device has members adapted to receive and hold the container close to the spray nozzle. The container may be detached and removed from the device and exchanged with another such container when refilling and changing paint type.
Thus, the invention is based on locating the paint source unit in proximity with the spray nozzle, to reduce the connection length between the paint source and the nozzle while the paint is applied. The device avoids the need to use long ring conduits that are susceptible to plugging and that require a comparatively high amount of power to pump, especially when using pumping water-born paints having a high viscosity. The device does not require a large number of hoses and valves for feeding paint of different colors to the nozzle, but facilitates color change easily through replacement of the paint container. A container may be used continuously for the same color, so that no cleaning of the container is required before refilling it with paint. No insulating problems occur when using water-borne paints in connection with electrostatic painting, since the paint container is isolated from devices external to the spray robot, such as external paint reservoir. The container also serves to insulate materials on opposing sides of the container.
According to a preferred embodiment of the invention, the device comprises a means adapted to dose paint from the container to the spray nozzle during the spray application. This dosing means is adapted to influence the inner volume of the container holding paint. Paint is pressed out of the nozzle, through and opening, by reducing the volume of space within the container for holding paint. Feeding paint in this way provides a very exact and reliable dosing of the paint through a simple means.
According to another preferred embodiment of the invention, the paint dosing means is adapted to act upon the container by compressing its volume from the outside. The dosing means does not come into contact with the paint and, therefore, no cleaning of the dosing means is required when the paint container is changed. This feature saves time as well as paint and cleaner.
According to another preferred embodiment of the invention, the container is compressible, and said dosing means is adapted to compress the container. By such compression, a very exact dosing of paint to the spray nozzle may take place.
According to another preferred embodiment of the invention, he container has a bellows-like construction for facilitating compression of the container. A very exact and uniform dosing of paint to the spray nozzle may be achieved by this.
According to another preferred embodiment of the invention, the container has a wall that is displaceable with respect to the other walls of the container, while maintaining a tight delimitation of the volume. The dosing means is adapted to act upon the displaceable wall to displace the paint and thereby supply paint to the nozzle in controlled doses. This embodiment makes it possible to achieve an exact dosing of paint that is fed to the spray nozzle by a simple means.
According to another preferred embodiment of the invention, the dosing means comprises a power member having a piston and a piston rod. This dosing means is adapted to act upon the container by compressing the volume of the container with the piston. This design for feeding paint in a dosed manner to the spray nozzle makes a very exact dosing possible.
According to another preferred embodiment of the invention, the container is elongated at the opening to form a feeding tube adapted to be held by said receiving members when inserted in the nozzle. By providing the container with a feeding tube that extends all the way into the spray nozzle, the need to clean the paint paths of the device will be reduced. Moreover, the paint feeding path that requires cleaning is restricted, at most, to the end of the spray nozzle located downstream of the feeding tube. With this feature, the paint loss will be minimized when changing to a paint of another color.
According to another preferred embodiment of the invention, the device is arranged in a spray application robot having a nozzle located at the free end of one robot arm. Receiving members form a space inside the robot arm and are adapted to receive said container. With this arrangement, the container may be safely held in place and protected against external influences. Additionally, this arrangement provides a very compact reservoir to draw paint from during the spray application.
According to another preferred embodiment of the invention, the dosing means is arranged inside the robot arm in a space adjacent to the receiving member space holding the paint container. Thereby the dosing means is protected against external damage and both the paint container and the dosing means are stored compactly inside the robot arm.
According to a very preferred embodiment of the invention, said robot arm is arranged to be opened so that the container may be inserted or removed from the space formed by the receiving members. One end piece of the robot arm pivots with respect to the rest of the arm, about an axis substantially perpendicular to the longitudinal axis of the arm. The end piece has a space formed by the receiving members for receiving the container. A space, for the dosing means is arranged in the part of the robot arm connected to the end piece. This configuration makes it very simple to insert and remove a paint container without the dosing means being in the way.
Further advantages of the invention will appear from the following description.